The scenario being set in the future requires the contrivance where the planet has a high density/gravity limiting the use of lighter than air/ flying machines. Obviously this is required to explain away the absence of flying craft in a future scenario.

How difficult would it be to incorporate aircraft into CC? Aren't airborne forces not much more than a combination of the characteristics of both fleets and armies other than they can attack virtually anywhere?

If aircraft were to be ever brought into the game, I suggest that they would act in such a manner:

1. They can only attack the armies defending an an enemy territory and not the country, so they can't invade by themselves.2. They would be unable to hold a country or defend or take a country by themselves3. They can transport troops onto friendly territory, paratrooper-style attacks possible but only at very high cost to the attackers to reflect the costly reality of airborne assault.